This invention relates to flame retardant polyester compositions. More particularly, this invention relates to flame retardant thermoplastic polyester compositions comprising a thermoplastic polyester and a flame retarding amount of the pentate salt of an amino-s-triazine and to a method for rendering thermoplastic polyesters flame retardant.
Thermoplastic polyesters and copolyesters are widely employed in a variety of applications such as for making injection molded parts, forming fiber and film structures, in structural foam applications and as blow-molded goods. The ready processability and toughness of these resins, and particularly of the copolyester and polybutylene terephthalate resins has been a major factor in their wide acceptance. Thermoplastic polyester resins are, however, generally regarded as flammable, with UL94 NVE burning properties. The use of additive flame retardants is therefore indicated where flame retardant properties are required.
Flame retarded polyester compositions containing halogen compounds or phosphorus compounds which exhibit self-extinguishing, UL V-O characteristics are well known. For some applications the use of halogen- or phosphorus-based additive flame retardants is not desirable. Some phosphorus compounds, for example, tend to plasticize polymers and alter the physical properties. Similarly, halogen-based flame retardants, whether used alone or in conjunction with synergists such as antimony oxides may alter key physical properties of the resin and limit the potential enduses. Recent, in U.S. Pat. No. 4,257,931, there was disclosed a method for flame retarding poly (1,4-butylene terephthalate) resins by incorporating a combination of a pentaerythritol diphosphonate and melamine pyrophosphate. Although the patentees' compositions are disclosed as being self-extinguishing and non-dripping, the process employs a substantial level of a diphosphonate compound which may be an economic disadvantage for many enduses. An alternative flame retardant for use in these resins would thus broaden the choices available to the resin compounder for meeting the demands of the market.